The product information no. W 13-7364, 4/1996 of the Klöckner-Moeller Company titled “Monitoring and detecting: reliable and safe, position switch AT” describes an electromechanical position switch. In a housing, there are mechanical switching contacts, for example, pairs of or individual contacts of break contacts and/or make contacts, and there is a butt tappet that can be slid lengthwise for direct mechanical actuation of the switching contacts. In order to be able to use the position switch in the most versatile manner possible, replaceable drive heads are placed in front of the butt tappets. Thus, as desired, a drive head with a swiveling lever, a roller lever, an adjustable roller lever or a torsion bar can be attached to the housing of the position switch.
An electronic-mechanical position switch is known from German utility model DE 202 03 214 U1. An actuation tappet, a potentiometer, a microcontroller and electronic switching contacts are arranged in a housing. The actuation tappet is coupled to the wiper of the potentiometer. When the tappet is actuated, a changing electric signal is fed to the microcontroller and this signal brings about a change in the state of the switching contacts when the signal exceeds or falls below a programmed threshold value. The switching contacts are connected to the clamp terminals on the output side. In order to set the switch-over point, it is proposed to program the threshold value via a programming connection or via a selector switch, or else to make a selection from a number of predetermined threshold values that are stored in a microcontroller. No information is provided as to how failures in the electronic system can be detected in order to prevent erroneous output signals from leading to erroneous control operations at the periphery of the position switch.
German patent DE 37 34 431 C2 describes a method for monitoring the state transition of final stage circuits for final control elements from the closed to the open state. During operation, the trip-on signals are periodically interrupted by test signals. Feedback to a microcomputer is sent from the final stage circuits and, if the state transition does not occur, said microcomputer ensures that the final stage circuits are permanently set to the open state. The test signals are shorter than the response-reaction time of the final control elements. The microcomputer is not monitored.